Pre-fabricated structural components strengthened with tensile reinforcements and method for production thereof

ABSTRACT

The prefabricated structural components strengthened by tensile reinforcements, preferably metal inlays, containing binders and aggregates, wherein said binder is an alkali water glass, and the aggregates have a broad grain size distribution like aggregates added to reinforced concrete.

The present invention relates to prefabricated structural components strengthened by tensile reinforcements, preferably metal inlays, containing binders and aggregates, and methods for the production thereof.

The most notorious structural components of this kind consist of reinforced concrete, which, although having proven very useful in many respects, is known to have the following drawbacks:

In the tensile zones of reinforced concrete, iron rods are generally employed which are circumferentially uniformly beaded with a wire lest they should be pulled out of the surrounding concrete upon tensile stresses. Another frequently employed form of metal inlays in reinforced concrete are bulged iron rods. The reason for this complicated structure is the completely missing adhesion between the cured cement and the steel surface.

Another drawback of Portland cement concrete is its property of always being more or less porous and filled with air cells. Although the porosity can be reduced by appropriately selecting the sieve curves of the aggregates, it cannot be completely avoided. This structure, which is open to diffusion, enables water and water vapor to permeate into the interior of the constructional body, so that an increase of the porosity and reduction of the adhesion between the concrete and the steel surface occur at temperatures around the freezing point of water.

In addition, the thus permeating water has the even more deleterious property of irreversibly corroding the metal inlays. Corroded metal inlays lose their tensile strength, which is an important and necessary property.

A further great disadvantage is the very poor refractoriness of all reinforced concrete constructions. Among other reasons, this is because cured Portland cement completely decays already at temperatures of from 400 to 450° C. and thus loses its important inner strength. However, according to DIN 4102 item 6.2.4, in the case of a fire, a fire temperature of 556° C. is reached already after 5 min.

But the iron rod inlays are also known to lose their inner strength from 500° C. A complete disintegration then occurs in the range around 750° C. Thus, a reinforced concrete construction loses its inner strength very quickly and without warning.

In order to somewhat reduce the permeability for water and the fire sensitivity, the law requires an additional coating of at least 50 mm of concrete. However, this layer is statically inefficient and thus is only an unnecessary load on the total construction.

Finally, a disadvantage of reinforced concrete parts is the fact that they cannot be homogeneously interconnected in a refractory way.

DD 286 807 A5 describes a method for increasing the tightness and strength of water glass concrete by impregnating the optionally reinforced structural component with liquid sulfur at a temperature of from 115 to 120° C.

Evidently, the inventors selectively attach importance to increasing the tightness and strength of “water glass concrete” by the impregnation with liquid sulfur, which is technically very complicated and economically expensive. Mention is made of “optionally reinforced structural components”. Increasing the strength of non-reinforced structural components is completely unimportant in building technology. Non-reinforced water glass concrete components have no tensile strength in bending, and this is the highest demand set on structural components; otherwise, the parts would merely be statically unimportant building boards. Further, the slight increase of strength due to the liquid sulfur is without any importance in terms of building technology even for such building parts. Building boards could be made thicker and stronger in compression simply by adding more Portland cement, or simply by a greater thickness.

This document by no means describes a structural component which is load-bearing, water-tight and has a particularly high refractoriness.

It was the object of the invention to eliminate these drawbacks of reinforced concrete and thus to provide highly loadable, highly refractory and water-tight structural components.

According to the invention, this object is achieved by prefabricated structural components strengthened by tensile reinforcements containing cured binders and aggregates, characterized in that said binder is an alkali water glass, and the aggregates have a grain size distribution common for aggregates in reinforced concrete, wherein the components are mixed, introduced into a mold and cured at 100 to 150° C., followed by annealing the structural components at a temperature within a range of from 500 to 700° C.

According to the invention, the aggregates added to the binder have a broad grain size distribution like the aggregates added to reinforced concrete. Thus, these are structural components which correspond to reinforced concrete in many respects, but in which the Portland cement has been replaced by an alkali water glass.

Alkali water glass, i.e., sodium and/or potassium silicate, is the only inorganic and thus highly refractory adhesive and thus the only efficient adhesive medium for the aggregates, especially quartz powder, but also for the tensile reinforcements, which are always necessary.

Alkali water glasses contain 15% free water and 15% chemically bound water on average. The free water evaporates slowly at ambient temperature, but more quickly at 100 to 120° C. or higher. Thus, the structural parts according to the invention can be prepared on site with molds as usual and allowed to dry slowly.

With the completion of the process of evaporation of the free water molecules, the binding function of the alkali water glass with the aggregates, the quartz fraction and the tensile reinforcements is essentially complete.

Reinforced concrete components of the usual kind prepared on site require a curing time of from 3 to 4 weeks before they can be utilized and walked on. For the structural components according to the invention, the time required is substantially shorter.

Now, for some time, in the building technology and economy, especially in reinforced concrete construction, a tendency has been observable away from preparing on site and towards industrial prefabrication in a hall. Thereafter, mounting is performed with cranes on site.

The advantages of this method include a better quality, independence of weathering influences and thus better quality controls as well as better supervision possibilities for the workers. The curing time of 3 to 4 weeks on site is also eliminated.

This system of the prefabrication of the structural components is also particularly advantageous for the structural components according to the invention, since these structural components can release their free water within a very short time in a range of from 100 to 150° C., especially from 120 to 150° C.

Typical embodiments of the structural components according to the invention and their constructive use are illustrated in more detail in the following Figures.

FIG. 1 shows the inner structure of the structural components according to the invention with the binder and aggregates in a highly enlarged representation. They do not contain any air cushions inside and exhibit a high density and high compression strength. For this reason, the structural components can even have a smaller and thus more light-weight and inexpensive design as compared to corresponding structural components made of reinforced concrete for the same static load. Due to their high refractoriness, the structural components can even be employed in melting furnace construction.

FIG. 2 schematically shows a structural component with metal inlays, in which 1 represents the structural component according to the invention made of aggregates and binder, 2 represents the thin adhesive mineral layer, and 3 represents tensile reinforcements consisting of rods or ropes.

FIG. 3 shows the course of inner static forces when such a structural component is under load.

FIG. 4 shows the case of loading for a uniform ceiling load in a tower block.

FIG. 5 shows the use of steel sheets instead of iron rods, the sheets being graduated in accordance with the inner static values. Of course, for these structural components too, the statics calculation of the specialists will determine the design of the constructive body, the number, size and shape of the tensile reinforcement, taking into account the inner forces occurring under load.

FIG. 6 shows a high-voltage current heating member coated on three sides for temperatures of between 100 and 150° C. in which a structural component according to FIG. 5 can be prepared. The inner wall of the coat is preferably provided with a release agent in order that the finished structural component can be easily taken out after drying.

FIG. 7 represents a proposition for the precise spatial adjustment of a steel sheet in a structural component according to FIG. 5.

FIG. 8 describes a proposition for a possible simplified production in which prefabricated narrow board-like support members are welded together for the intended design.

Here, the economically advantageous and statically efficient welding of the prefabricated thin plates according to the invention in the top region, which has only compression strength, has a particularly useful effect.

FIG. 9 shows a different design, which is statically interesting because it requires less material and yet meets the demanded requirements.

FIGS. 10 to 12 show further examples of structural components which are welded together from individual parts in a material-saving way and yet exhibit high stability.

Further, the structural elements can have the shape of round or polygonal tubes.

The idea of the production of these structural components according to the invention in an industrial prefabrication is schematically shown in FIG. 6. For example, 2 are electrically heated walls, and the mineral composition 1 is filled in between. 3 is an adhesive medium against the adhesion of the alkali silicate, for. example, a sheet of polytetrafluoroethylene.

For shortening the drying time of the free water molecules, composition 1 can be preheated.

In test experiments, it was established that the adhesion force between steel surfaces and the mixture of the alkali silicate and quartz sand is surprisingly high, namely 639 kN/m². An optimum bonding of the steel tensile reinforcement in this mixture and thus very efficient inner statics of the structural components according to the invention are thereby achieved.

In statics, there is a principle of the equilibrium of the external forces with which the structural component is loaded and the inner forces of the component. This is schematically represented in FIG. 4. A supporting beam on two supports bears a uniform load per unit area. FIG. 3 shows the course of the inner forces in the case of such a load. In the bottom part, the necessary sizes of the tensile reinforcements can be seen. In exact accordance with these requirements, the tensile reinforcements are employed as shown in FIG. 5. Instead of steel wires, steel sheets or ropes may also be employed according to the invention.

This precise determination of the tensile reinforcement meets the requirements and represents an essential progress over the traditional reinforced concrete construction.

Due to its very high adhesion force, the suspension of quartz sand and alkali silicate is also employed for bonding or welding prefabricated structural components together.

In addition, there is another optimum application of this increased adhesion force. As shown in FIG. 5, four plate-like ready-made structural components can be bonded with the mineral suspension to form a new structural component having a higher carrying force and homogeneously welded.

These means thus enable a new prefabrication of tensile-reinforced structural components which is particularly economic. The thin layer of adhesive is dried at 100° C. in 2 to 3 min, the individual plates can be prepared in stock in different thicknesses, reinforcements and lengths, especially in times of low degrees of utilization of the production sites. Thus, structural elements can be employed which are prepared in stock and can be used for all designs. Thus, each order can be completed within short delivery times.

This great flexibility of the preparation is a great economical advance and contributes to the fact that the customer can be served quickly and reliably.

Further examples of flexibility are schematically shown in FIGS. 7 to 12.

FIG. 7 shows the interlacing and interlocking of tensile reinforcements in two directions. FIG. 8 shows a composition in accordance with the external forces of four structural components into a new one. FIG. 9 shows a box-shaped support as a constructive structural component which is also adapted to the static requirements and the respectively desired design. One particular possible design in a particular case is shown in FIG. 10.

In particular cases, the aesthetics of a structural component can be important. In the usual reinforced concrete, the gray-green color of the Portland cement is always predominant. The mixture of quartz powder and bodies according to the invention is light in color, almost white. If aluminum hydroxide, for example, is added as a filler composition, then the ready-dried structural component is almost purely white. However, if desired, any other color powder may be added to reach the final color. On this basis, all colors are displayed clear and bright.

However, in addition to this aesthetic design, the preventive fire protection of these supporting structural components is mostly even more important.

In the structural components according to the invention, the chemically bound water remains in the alkali silicate after the first stage of evaporation. This chemically bound water will escape only in a temperature range of from 500 to 700° C. At the same time, this process involves a cooling effect of a particularly favorable kind. In the case of a fire, the passage of the fire temperature is very significantly delayed. The temperature passage through a plate of 1 cm is slowed down by about 30 to 40 min. According to the invention, the annealing of at least the surface of the structural elements serves for ensuring external tightness. In the case of a fire, the above mentioned chemically bound water can then evaporate from deeper-lying layers and bring about the cooling effect.

In the above mentioned use of aluminum hydroxide, a welcome additional cooling effect is achieved by the evaporation of the water molecules contained therein. The passage of the fire temperatures is delayed by another 15 to 20 min when aluminum hydroxide is used.

Thus, the heat is caused to enter the structural component at a significantly slower rate. After the escape of this chemically bound water, the water glass still keeps its adhesive function and is also capable of stably holding the aggregates together. The structural components according to the invention are thus highly refractory and withstand a fire of many hours.

Further, the water glass annealed at high temperatures also keeps its adhesion with the steel surface and thus with the tensile reinforcements, so that the tensile strength is maintained.

The adhesion forces are so strong that usual rods, ropes or sheets may also be used as tensile reinforcements, such as metal inlays. It is not necessary to employ iron rods which are either beaded or bulged as with reinforced concrete. The adhesion force between steel surfaces and the mixture of aggregates and binder according to the invention was established to be 639 kN/m².

At normal temperatures, the structural components according to the invention are completely impermeable to water or water vapor, so that no corrosion of the metal inlays occurs. Thus, the metal inlays can not only have a different and simpler shape, they may also be incorporated in the form of ropes or sheets which yield higher tensile strengths at a lower weight. When the aggregates consists of a highly refractory material, such as quartz sand, the structural components according to the invention are volume-resistant up to 2100° C.

In FIG. 10, another example of the design of the structural components according to the invention is schematically demonstrated. What can be clearly seen is the well-aimed welding together of the prefabricated thin structural components to give a statically particularly efficient box form which can be subjected to a static load from all sides.

This interesting design can be realized only by the high adhesive force of the mixture of quartz sands and sodium silicate.

Another design example is shown in FIG. 12: a design like the known steel construction of a sheet metal support. This design in steel construction previously required many rivets and a high expenditure in wages, and now it requires linear welding.

Such a design of a load-bearing structural component according to the invention has the following properties which are superior to those of a steel sheet construction:

In the zones of compression stresses, the mineral media are economically and technically superior to steel.

The structural component according to the invention does not exhibit any corrosion.

The prefabrication of the individual parts as well as the welding together on site is significantly more favorable economically.

For a steel support to remain stable for 90 min to 120 min in the case of a fire, it must be reliably protected with fire protection plates from all sides.

The structural component according to the invention withstands the fire temperatures according to DIN 4102 of from 1100 to 1200° C. for more than 120 min; as tested, it can withstand from 1500 to 2000° C.

The prominent property of utilizing the adhesive forces of the mineral component is again represented in FIG. 13 and FIG. 14.

FIG. 13 schematically shows the parts which are prefabricated and are to be welded together on site into a new design, for example, a framework construction.

FIG. 14 schematically shows the new shape.

The two surfaces A-B-C-D are completely brushed with the adhesive mixture of water glass and quartz powder or sand, and then the two parts are joined. After the drying process, which can be accelerated by electric mats on both sides, this rectangular molded part is completely stable mechanically and has a very high loadability.

If such a design was realized with steel parts, full-area welding of these parts would not be possible, but only linear welding would be possible, and this would mean a substantially lower static bonding.

The preparation of the structural components according to the invention is effected, for example, by mixing the components and introducing them into molds and curing at 100 to 150° C. The evaporation of the free water molecules requires only a few minutes. This is a considerable advantage over the usual curing process of reinforced concrete over 3 to 4 weeks.

Even the drying process and thus the consolidation of structural components according to the invention directly on site requires days, but not weeks as in the traditional reinforced concrete construction.

After the first drying process, the structural components according to the invention still have some sensitivity towards water. The dried alkali silicate is not sufficiently resistant to constant contact with water, or when employed underwater. However, this is not disadvantageous when used on the lower side of story ceilings. But it may be disadvantageous already with supports according to the invention in rooms.

Therefore, the surfaces of such supports are preferably protected with water-repellent paints or water-resistant linings. The method according to DE 39 23 284 C1 is also suitable. Thus, the aggregates are homogeneously mixed with an alkali silicate and subsequently knife-coated uniformly onto a sheet of polytetrafluoroethylene in a thin layer having a thickness of from 1 to 3 mm. In a first stage, drying is performed at 100 to 150° C. for the free water molecules to escape. This is followed by annealing at a temperature of from 550 to 700° C. This yields uniformly strong and dense plates having an almost polished surface which can be provided with any color in bulk and employed with an appearance similar to that of a natural rock plate. A thin steel wire mesh can be incorporated lest these thin plates should be too sensitive; cf. DE 39 23 284 C1. The tensile composite strength in bending of such plates is excellent. They can be readily bonded with the structural component according to the invention and provide sufficient protection towards water and moisture.

The bonding may preferably be effected with water glass, which provides for a homogeneous and durable bonding. In the same way, the prefabricated structural elements may also be welded together on site and joined, so that the contact areas and joints of the structural components will then also have the desired refractoriness.

Thus, the structural components according to the invention without a water- and weather-resistant protection layer can be excellently employed mainly in the interior of buildings. In the case of a fire, the escape of the chemically bound water results in a cooling process and at the same time in a consolidation of the structural components in the highly refractory range. In contrast, if it is bonded and lined with a plate having a thickness of at least 2 mm and having been annealed at a high temperature, a structural component which may also be universally employed in the outdoor field is formed from parts which are also prefabricated.

One particularly important application of this very thin plate which is tight towards water and water vapor, resistant to ultraviolet radiation, highly refractory and bulk-colored is as a protective coating of reinforced concrete constructions in the outdoor field, for example, for motorway and road bridges. The bad property of the concrete, i.e., its water-permeability with corrosion of the steel inlays, is thus finally eliminated. This also eliminates the need for the expensive repair work required later.

Thus, the structural components according to the invention have the following important properties for the construction field:

-   -   complete impermeability to water, the steel reinforcement thus         remaining reliably protected from corrosion;     -   on a tension side of the structural components according to the         invention, a particularly efficient dense arrangement of the         steel reinforcements is possible because the quartz/silicate         mixture has a particularly favorable adhesion with the steel         surface;

the very high strength with 2000° C. towards fire temperatures which rise to at most 1200° C.

By means of the invention, it is possible to reliably shield, for example, nuclear reactors with these structural components against burning crashing airplanes and thus avoid a worst case scenario. Such a reliable protection cannot be reached with the current reinforced concrete and steel constructions. 

1. Prefabricated structural components strengthened by tensile reinforcements containing cured binders and aggregates, characterized in that said binder is an alkali water glass, and the aggregates have a grain size distribution common for aggregates in reinforced concrete, wherein the components are mixed, introduced into a mold and cured at 100 to 150° C., followed by annealing the structural components at a temperature within a range of from 500 to 700° C.
 2. The structural components according to claim 1, characterized in that the metal inlays are in the form of rods, ropes and/or sheets.
 3. The structural components according to claim 1, characterized by being externally coated with a waterproof and weather-resistant protection layer.
 4. The structural components according to claim 3, characterized by being externally coated with a plate having a thickness of at least 2 mm and having been annealed at 500 to 700° C. and prepared from water glass and fillers selected from the group consisting of Al₂0₃, SiO₂ and/or carbon.
 5. A method for preparing the structural components according to claim 1, characterized in that the components are mixed, introduced into a mold and cured at 100 to 150° C., followed by bonding the annealed plates with the structural component using water glass.
 6. A method for preparing the structural components according to any of claim 1, characterized by having the shape of round or polygonal tubes. 